1. Field of the Invention
The present invention relates to a coil apparatus and a non-contact power transmission apparatus.
2. Related Background Art
Magnetic resonance type power transmission which is capable of supplying power with high efficiency over relatively moderate distances by matching the resonance frequencies of a power transmission (power feed) side and a power receiver side has received attention as a non-contact power transmission technology. This technology is capable of transmitting power at high efficiency when the resonance frequencies of the power transmission side coil and the power receiver side coil are matching.
In power transmission by magnetic resonance, it is known that the power transmission efficiency and the transmission distance are dependent on the Quality Factor (Q) of the coil and the coupling coefficient k of the two coils. The coupling coefficient between the coils becomes lower as the distance between the power transmission side coil and the power receiver side coil becomes greater, but if the coil has a high Q factor, then power transmission is possible even if the coupling coefficient is low. On the other hand, when coils having a high Q value and the same or similar resonance frequencies are brought close together, the two coils affect each other and divergence in the resonance frequencies occurs, and therefore it is necessary to control the resonance frequencies.
In response to technological problems of this kind, for example, Japanese Patent Application Laid-open No. 2010-130878 describes an example in which power is transmitted with high efficiency by matching the resonance frequencies of the power transmission side coil apparatus and the power receiver side coil apparatus. When a coil is caused to resonate by the coil inductance and stray capacitance, with the object of matching the resonance frequencies of the coil apparatus on the power transmission and power receiver sides, there may be divergence in the resonance frequencies due to variation in the coil, or the like, but the invention described in Japanese Patent Application Laid-open No. 2010-130878 discloses technology in which a variable capacitor is added externally to the inductance of the coil and the resonance frequency is adjusted by adjusting the variable capacitor. In the embodiment described therein, there is no problem if the position is fixed, but re-adjustment of the resonance frequency is necessary if there has been even slight positional divergence.
Furthermore, Japanese Patent Application Laid-open No. 2009-268181 describes a composition which comprises a resonance frequency adjustment circuit for adjusting and setting the resonance frequency, and proposes controlling the resonance frequency by connecting a variable capacitor and/or a variable inductor to the transmission coil. If a variable capacitor or a variable inductor is adjusted in the transmission coil, then there is a risk of this giving rise to reduction in the Q value due to the effects of external elements.
Furthermore, Japanese Patent Application Laid-open No. 2010-93902 discloses an example in which the Q values of the power transmission coil and the power receive coil fall and the efficiency declines, if power is transmitted by a non-contact method between a transmission side coil which constitutes a resonance circuit and a power receiver side coil which constitutes a resonance circuit, but decline in the efficiency is reduced if a resonance circuit which is formed by a third coil as a control coil and a capacitor is inserted between the transmission side coil and the receiver side coil so as to be magnetically coupled with both coils.
However, in the compositions described in Japanese Patent Application Laid-open No. 2010-130878, Japanese Patent Application Laid-open No. 2009-268181 and Japanese Patent Application Laid-open No. 2010-93902, divergence in the resonance frequency of the transmission coils of the power transmission side coil apparatus and the power receive side coil apparatus has not been investigated sufficiently.
For example, in Japanese Patent Application Laid-open No. 2010-130878, in the embodiment described therein, there is an issue in that, although there is no problem if the position is fixed, re-adjustment of the frequency is necessary if there has been even slight positional divergence. Furthermore, in Japanese Patent Application Laid-open No. 2009-268181, if a variable capacitor or a variable inductor is adjusted in the transmission coil, then there is a risk of this giving rise to a fall in the Q value due to the effects of external elements.